Frequency control devices are known to include temperature-compensated crystal oscillators (TCXO). A typical TCXO utilizes a piezoelectric material and temperature compensation circuitry to provide a reliable and stable oscillator output, for example, for high frequency wave forms under varying environmental conditions. These devices are commonly found in portable radio frequency (RF) communication equipment, such as cellular telephones, pagers and wireless modems. As consumer demand continually drives down the size of cellular telephones and other communications equipment, the need for TCXO's having smaller dimensions and reduced weight has become even greater.
FIG. 1 is a perspective view of a prior art TCXO 10. The TCXO 10 includes a piezoelectric element 12, temperature compensation circuitry in the form of an integrated circuit (IC) 14 and chip capacitors 16, input/output pads (not shown), and a device lid 18. A hermetically sealed environment 20 is formed when the lid 18 and housing 22 are attached.
When a voltage is applied across the piezoelectric element 12, the element 12 resonates at a certain oscillator output. The resonant frequency of the piezoelectric element can change or drift about a nominal frequency, responsive to the changes of temperature in the housing 22. Typically, a temperature sensing device which could be included in the IC provides information to the temperature compensation circuitry regarding the environment 20. As the temperature within the environment 20 fluctuates, the temperature compensation circuitry suitably modifies circuit parameters to minimize frequency drift in the oscillator output.
The height, width and depth of the TCXO 10 are dependent upon the piezoelectric element, temperature compensation circuitry, integrated circuit 14 and chip capacitors 16 in the housing 22. That is, the overall size of the housing 22 and lid add to the overall dimensions of the TCXO 10. Typical dimensions for the TCXO 10 are about 8.89 mm.times.8.89 mm.times.2.79 mm.
While these dimensions may appear to be small, the demand for smaller cellular telephones and other electronic products necessitates TCXO's having even smaller physical dimensions. Therefore, a substantial need for frequency control devices which overcome prior art dimensional limitations, and which meet or exceed the appropriate performance requirements or criteria of their larger counterparts are needed.
There is also a need for: (i) a package or housing for frequency control devices which allows the piezoelectric element to be housed separately or to be isolated from the other components without sacrificing space, to minimize the possibility of cross-contamination of the components; and (ii) a mass producable package which can simplify frequency tuning and hermetic sealing.